In life science research and medical examination, it is generally necessary to detect a component of interest which has extremely small content in samples, for example, Circulating Tumor Cells (CTCs) in human peripheral blood. CTCs are tumor cells which enter into peripheral blood circulation of cancer patients spontaneously or by clinical operation. Detection of tumor cells in peripheral blood may forebode tumor metastasis. It has been proven in current research that CTCs can predict progression free survival and overall survival for various tumors including breast carcinoma, prostate carcinoma, colon carcinoma, lung carcinoma, ovarian carcinoma, etc., reveal metastasis mechanism of tumors, and may have potential clinical significance in tumor staging, diagnosis and making therapeutic scheme. However, on the other hand, CTCs have extremely small amount in peripheral blood compared with erythrocytes and leukocytes. For example, there may exist one CTC per 5-10 million healthy blood cells. Therefore, such content of interest as CTC is so scanty that it is important to provide an enriching and detecting technique.